Domestic heating appliance



June 11, 1963 G. w. SCHAUER, JR 3,093,722

DOMESTIC HEATING APPLIANCE Original Filed June 29, 1960 CONTACTSPOSITION PREHE T X X X X=CLOSED C= CYCLING IO Q r Elm-4| INVENTOR.George W Schaue; Jr

H/s Attorney Unite s atent dice 3,093,722 DOMESTIC HEATING APPLIANCEGeorge W. Schauer, J12, Dayton, Ohio, assignor to General MotorsCorporation, Detroit, Mich, a corporation of Delaware Continuation ofapplication Ser. No. 39,546, June 29, 1960. This application Feb. 23,1962, Ser. No. 176,860 11 Claims. (Cl. 2l9--20) This invention relatesto a domestic appliance and more particularly to an improved ovenroasting control circuit for an electric range. This is a continuationof my copending application Serial No. 39,546, filed June 29, 1960, nowabandoned.

Early studies have shown that certain advantages occur in roasting meatsfor extended periods at relatively low temperatures. The results of suchstudies have proven that cheaper cuts of meat can be roasted to a tenderdoneness with less waste since the roasting is done at temperaturesbelow approximately 170 F. With low temperature roasting, timing neednot be accurate; the important thing is to allow enough time for thesize out being roasted. Protein does not toughen. The gelatin issoftened and made sufliciently tender to eat without melting. Thus, thejuices are kept in the meat and there is relatively little loss inweight. The longer the meat cooks, the more tender it becomes.

At temperatures above approximately 170 F., there appears to be somechemical reaction which toughens the protein in the meat. If meats arecooked too long at high temperatures, the connective tissue of meat(gelatin) melts, the juices are lost, and there remains only tough,stringy, d-ry fibers. Although the desirability of such low temperatureroasting has been known before, no system has been embodied in adomestic range for the purpose of putting into practice these lowtemperature roasting concepts. Thus, it is an object of this inventionto provide an improved control circuit for an electric oven.

Accordingly, it is an object of this invention to provide an automaticlow temperature roasting control circuit which will provide in an oven abrief period of high temperature wherein the meat can be browned and thejuices sealed in followed by an extended period at temperatures belowapproximately 170 F.

It is also an object of this invention to incorporate a timing system inconjunction with a low temperature roasting control circuit such thatthe low temperature control circuit becomes effective only afiter apredetermined period of high temperature.

A further object of this invention is the provision of a timing meansfor a low temperature control circuit which may be preset in accordancewith the weight and type of meat to be roasted.

A more general object of this invention is the provision of an ovencontrol circuit with a low temperature thermostatic means, a hightemperature thermostatic means and timing means for selecting one or theother of said thermostatic means.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawing wherein a preferred embodiment of the present invention isclearly shown.

In the drawing:

FIGURE 1 is -a schematic wiring diagram of this invention; and

FIGURE 2 is a cycle chart showing the positioning of the various switchcontacts in the diagram of FIGURE 1.

In accordance with this invention and with reference to FIGURE 1, aschematic wiring diagram of the proposed control circuit for lowtemperature roasting is set forth.

FIGURE 2 shows a cycle chart indicating the specific open, closed orcycling condition of the various contacts depicted in FIGURE 1. Thecircuitry is proposed for use with an oven 10 which includes a broilheating unit 12 and a bake heating unit 14. A conventional thermostat,shown generally at 16, is utilized to control the temperatures withinthe oven 10 during normal high temperature baking operations. Thethermostat 16 includes a pair of contacts A and B opened and closed byswitches 15, :17 respectively. The switches 15, 17 are cycledintermittently by a hydraulic bellows l8 motivated by way of a capillarytube 20 and a sensing bulb 22 within the oven 10. The rate at which thecontacts A and B are cycled is dependent upon the presetting of astandard oven temperature control knob 24, the preset temperature beingsensed by the bulb 22 within the oven. Thus, if the knob 24 is set for325 F., the contacts A and B will open and close to maintain theselected temperature (325 F.) within the oven. The thermostat 15 alsoincludes interlock contacts C and D for selectively connecting the broilunit 12 and the bake unit 14- for either 118 volt or 236 volt operation.

The foregoing description has set forth only the conventional hightemperature responsive oven control circuit. To provide a lowtemperature roasting control circuit, certain auxiliary equipment mustbe added. The standard thermostat 16 in use today is calibrated foraccuracy in the range from 250 F. to approximately 500 F. As aforesaid,the advantages of low temperature roasting are attained only below the170 F. mark where the standard thermostat .16 is least accurate. Forthis reason, a low temperature thermostat 30 is included and suppliedwith a set of low temperature controls E intermittently opened andclosed by a switch 31 operated by a hydraulic bellows 32 through acapillary tube 34 leading to a temperature sensing bulb 36 Within theoven 10. The low temperature thermostat 30 is preset to maintain theoven 10 at approximately 160 F. At this low temperature the meat willroast slowly without waste and without the meat fibers becomingtoughened.

The control circuit is completed by the addition of a timer 40 whichcooperates with the low temperature thermostat 30 and the standard ovenhigh temperature thermostat 16 to selectively place one or the other inthe control circuit for the oven heating elements 12 and 14. The timer40 is comprised of a timer motor 42, a timer motor cam 44, a thermostatselector cam 46, a bake unit power supply cam 48 and a low temperaturecontrol knob 50. Note that the control knob 50 may be calibrated eitherin time, as at 52, or in weight of the roast, as at 54. The timer motorcam 44 acts to position a cam actuated switch 56 to open and close acontact K in accordance with the energization of the timer motor 42.Further, the thermostat selector cam 46 actuates a cam switch blade 58between a low temperature thermostat contact F and a high temperaturethermostat contact G. When the switch blade 58 is against the contact G,the standard thermostat 16 is in series electrical flow relationshipwith the broil and bake heating elements 12 and 14, respectively.Conversely, when the cam actuated switch blade 58 is in engagement withthe contact F, the low temperature thermostat 30 is placed into controlrelationship with the oven heating elements. Lastly, the bake heatingelement cam 48 positions a cam actuated switch 60 between a high voltagecontact I and a low voltage contact H. When the bake heating element '14is energized through the contact I, it operates on 236 volts, thissituation occurring during preheat operation. However, when the camactuated switch 60' is closed on contact H, the bake heating element 14is energized for a 118-volt operation, this situation occurring duringlow temperature roasting.

FIGURE 2 may be referred to in determining the position of the varioussets of contacts A, B, C, D, E, F, G, H, J and K during the OFF, PREHEATor LOW portions of the low temperature roasting cycle. In operation, letus assume that a housewife is prepared to cook an inexpensive,five-pound roast using the low temperature circuitry of this invention.She will place the roast Within the oven 10 and set the standardthermostat control knob 24 for approximately 325 F. At the same time,she will position the browning or low temperature time knob 5a to theweight of the meat or roast (say five pounds on the dial portion 54 orapproximately ninety minutes of the dial portion 52). The lowtemperature control circuitry is now placed into the PREHEAT position.Contacts C, D, G, I and K are closed positively while contacts A and Bare cycling in accordance with the temperature within the oven asprescribed by the setting on dial 24, 325 F. in this instance. Thus,timer motor 42 is energized from L line 70, contact K, cam actuatedswitch 56, the timer motor 42 to the neutral (N) side of the powersupply. As the cycle is initiated, the heating elements 12 and 14 willbe energized as follows: from L through line 72, contacts A, line 74,contact G, cam actuated switch blade 58 to the junction 76 of the broilheating element 12 and the bake heating element 14. From this point '76,the broil element 12 will be energized by way of line 78, contacts D tothe neutral side of the line N, thus placing the broil unit 12 on 118-volt operation.

At the same time, the bake heating element 14 will be energized from thejunction point 76 by way of the cam actuated switch blade 60, thecontact], contacts C, cycling contacts B to the other side of the line Lthereby placing the bake heating element 14 on 236-volt operation forrapid preheat of the oven 10. The temperature within the oven 10 willquickly reach the presetting on the knob 24, namely 325 F., and thecontact A and B will cycle to maintain the presetting for the length oftime prescribed on the browning time knob Sit.

At the expiration of the time programmed by the knob 50 (ninety minutesin the case of our five-pound roast), the circuitry for extended lowtemperature roasting will automatically be established. Thus, thecontact K will be opened to deenergize the timer motor 42.Simultaneously, the contact G will be opened and the contact F closed toplace the low temperature thermostat into the oven heating elementcicruit instead of the high temperature thermostat 16. Lastly, the cam48 will reposition the switch 69 from contact I to contact H toestablish l18-volt power supply to the bake heating element 14. The lowtemperature roasting operation thus established will then continue withboth heating elements 12 and 14 energized for ll8-volt operation. Theheating elements will be cycled in accordance with the temperaturesensed by the bulb 36 and transmitted to the bellows 32. Since thethermostat 3% is set for approximately 160 F. operation, thetemperatures within the oven it will be maintained at this low valuethroughout the balance of the low temperature roasting operation. Thislow temperature roasting operation may continue for approximately 24hours before the roasting process is completed. No provision is includedfor terminating the low temperature roasting cycle. However, thisomission is not believed significant since a leeway of two or threehours in either direction while using the low temperature roastingtechnique of this invention is acceptable without significantly changingthe end result. The meat will be cooked with a minimum loss of weightand with a degree of tenderness not formerly possible at theconventional higher roasting temperatures.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. An automatic roasting control for effecting a preheat cookingoperation and a low temperature cooking operation in an oven having abake heating element and a broil heating element comprising; a powersupply; a low oven temperature thermostat having a low temperatureswitch responsive to temperatures in said oven; a high oven temperaturethermostat having first and second switches responsive to temperaturesin said oven; a timing means having a thermostat selector cam actuatedswitch connected to said heating elements and operating between a lowtemperature thermostat contact and a high temperature thermostat contactand a bake heating element power supply cam actuated switch connected tosaid bake heating element and operating between a high voltage contactand a low voltage contact; first circuit means connecting said powersupply, said low temperature switch and said low temperature thermostatcontact; second circuit means connecting said power supply, said secondswitch and said high temperature thermostat contact; third circuit meansconnecting said power supply, said first switch and said high voltagecontact; fourth circuit means connecting said power supply to said lowvoltage contact; and fifth circuit means connecting said power supplyand said broil heating element; said timing means adapted to close saidhigh temperature thermostat contact and said high voltage contact duringsaid preheat cooking operation; and said timing means being adapted toclose said low temperature thermostat contact and said low voltagecontact during said low temperature cooking operation.

2. An automatic roasting control for effecting a preheat cookingoperation and a low temperature cooking operation in an oven having abake heating element and a broil heating element comprising; a powersupply having first and second line conductors and a neutral; a low oventemperature thermostat having a low temperature switch responsive totemperatures in said oven; a high oven temperature thermostat havingfirst, second, third and fourth switches; said first and second switchesbeing responsive to temperatures in said oven during said preheatcooking operation and closed during said low temerature cookingopertion; said third and fourth switches being closed during both ofsaid operations; a timing means having a timer motor, a cam shaftoperated by said timer motor, a timer motor cam shaft actuated switchconnected to said timer motor, a thermostat selector cam shaft actuatedswitch connected to said heating elements and operating between a lowtemperature thermostat contact and a high temperature thermostat contactand a bake heating element power supply cam shaft actuated switchconnected to said bake heating element and operating between a highvoltage contact and a low voltage contact; a timer motor cont-actselectively engageable by said timer motor cam shaft actuated switch andconnected to one of said first and second line conductors; first circuitmeans connecting said neutral and said timer motor; second circuit meansconnecting said first line conductor, said low temperature switch andsaid low temperature thermostat contact; third circuit means connectingsaid first line conductor, said second switch and said high temperaturethermostat contact; fourth circuit means connecting said second lineconductor, said first switch, said third switch and said high voltagecontact; fifth circuit means connecting said neutral to said low voltagecontact; and sixth circuit means connecting said neutral, said fourthswitch and said broil heating element; said timing means adapted toclose said high temperature thermostat contact, said high voltagecontact and said timer motor contact during said preheat cookingoperation; and said tiniing means being adapted to close said lowtemperature thermostat contact and said low voltage contact during saidlow temperature cooking operation.

3. A control circuit for an oven having a bake heating element and abroil heating element in parallel circuit relationship comprising, ahigh temperature thermostat accurately responsive to high tem eraturesin said oven, a

low temperature thermostat accurately responsive to low temperature insaid oven, said thermostats being in parallel circuit relationship witheach other and in series circuit relationship with said heatingelements, first switch means for connecting one of said thermostats withsaid heating elements, second switch means for selectively connectingsaid broil heating element for high or low heat output, third switchmeans for selectively connecting said bake heating element for high orlow heat output, and timer means for controlling certain of said switchmeans in a manner to energize said broil heating element for low heatoutput and said bake heating element for high heat in series with saidhigh temperature thermostat during a first operation and said timermeans automatically terminating said first operation and controllingcertain of said switch means in a manner to energize said broil heatingelement for low heat output and said bake heating element for low heatoutput in series with said low temperature thermostat during a secondoperation.

4. A control circuit for an oven having a bake heating element and abroil heating element in parallel circuit relationship comprising, ahigh temperature thermostat accurately responsive to high temperaturesin said oven, a low temperature thermostat accurately responsive to lowtemperatures in said oven, said thermostats being in parallel circuitrelationship with each other and in series circuit relationship withsaid heating elements, first switch means for connecting one of saidthermostats with said heating elements, second switch means forselectively connecting said broil heating element for high or low heatoutput, third switch means for selectively connecting said bake heatingelement for high or low heat output, and timer means for controllingsaid first and third switch means in a manner to energize said broilheating element for low heat output and said bake heating element forhigh heat in series with said high temperature thermostat during apreheat operation and said timer means automatically terminating saidpreheat operation and controlling said first and third switch means in amanner to energize said broil heating element for low heat output andsaid bake heating element for low heat output in series with said lowtemperature thermostat during an extended low temperature operation.

5. In combination with an oven, a circuit for low temperature roastingin said oven comprising, a broil heating element and a bake heatingelement in said oven, a high and low voltage power supply, a firstthermostat calibrated for a first temperature range and selectivelyconnected to one side of said heating elements, a second thermostat inparallel circuit relationship with said first thermostat and calibratedfor a second temperature range higher than said first temperature rangeand selectively connected to said one side of said heating elements,means for connecting said thermostats to one side of said high and lowvoltage power supply, first means for selectively completing a circuitfrom the other side of one of said heating elements to the other side ofsaid high or low voltage power supply, second means for connecting theother side of the other of said heating elements to said low voltagepower supply, and a timer for automatically selectively connecting oneof said thermostats to said one side of said heating elements and forswitching said other side of one of said heating elements from said highvoltage power supply to said low voltage power supply at the end of apredetermined time period.

6. In combination With an oven, a circuit 'for low temperature roastingin an oven comprising, a heating element in said oven, a high and lowvoltage power supply, a first thermostat calibrated for a firsttemperature range and selectively connected to one side of said heatingelement, a second thermostat in parallel circuit relationship with saidfirst thermostat and calibrated for a second temperature range higherthan said first tem perature range and selectively connected to one sideof said heating element, means for connecting said thermostats to oneside of said high and low voltage power supply, means for selectivelyconnecting the other side of said heating element to the other side ofsaid high or low voltage power supply, and a timer for automaticallyselectively connecting one of said thermostats to one side of saidheating element and for switching Said other side of said heatingelement from said high voltage power supply to said low voltage powersupply at the end of a predetermined time period.

7. In combination with an oven, a circuit for low temperature roastingin an oven comprising, a heating element in said oven, a high and lowvoltage power supply, a first thermostat calibrated for a firsttemperature range and selectively connected to one side of said heatingelement, a second thermostat in parallel circuit relationship with saidfirst thermostat and calibrated for a second temperature range higherthan said first temperature range and selectively connected to one sideof said heating element, means for connecting said thermostats to oneside of said high and low voltage power supply, means -for selectivelyconnecting the other side of said heating element to the other side ofsaid high or low voltage power supply, and a timer for automaticallyselectively connecting one of said thermostats to one side of saidheating element and for switching said other side of said heatingelement from one of said high or low voltage power supply to the otherof said high or low voltage power supply at the end of a predeterminedtime period.

8. A control circuit for an oven having a first heating element and asecond heating element in parallel circuit relationship comprising, ahigh temperature thermostat accurately responsive to high temperaturesin said oven, 2. low temperature thermostat accurately responsive to lowtemperatures in said oven, said thermostats being in parallel circuitrelationship with each other and in series circuit relationship withsaid heating elements, first switch means for connecting one of saidthermostats with said heating elements, second switch means .forselectively connecting said second heating element for low heat output,third switch means for selectively connecting said first heating elementfor high or low heat output, and timer means for controlling certain ofsaid switch means in a manner to energize said second heating elementfor low heat output and said first heating element for high heat inseries with said high temperature thersostat during a first operationand said timer means automatically terminating said first operation andcontrolling certain of said switch means in a manner to energize saidsecond heating element for low heat output and said first heatingelement for low heat output in series with said low temperaturethermostat during a second operation.

9. A control circuit for an oven having a first heating element and asecond heating element in parallel circuit relationship comprising, ahigh temperature thermostat accurately responsive to high temperaturesin said oven, a low temperature thermostat accurately responsive to lowtemperatures in said oven, said thermostats being in parallel circuitrelationship with each other and in series circuit relationship withsaid heating elements, first switch means for connecting one of saidthermostats with said heating elements, second switch means forselectively connecting one of said heating elements for low heat output,third switch means for selectively connecting the other of said heatingelements for high or low heat output, and timer means for controllingcertain of said switch means in a manner to energize said one of saidheating elements for low heat output and said other of said heatingelements for high heat output in series with said high temperaturethermostat during a first operation and said timer means automaticallyterminating said first operation and con-trolling certain of said switchmeans in a manner to energize said one of said heating elements for lowheat output and said other of said heating elements tor low heat outputin series with said low temperature thermostat during a secondoperation.

10. In combination with an oven, a control for oven heating means in alow temperature roasting circuit comprising, a first thermostat having afirst cycling switch in series with said'heating means, said firstcycling switch means preset to cycle said heating means at a fixedpredetermined temperature in said oven and calibrated to respondaccurately to low temperatures in said oven, a second thermostat havinga second cycling switch in series with said heating means and inparallel With said first cyclingswitch, said second cycling switchcalibrated to respond accurately to high temperatures in said oven, andtiming means for selectively placing one of said switches in controlrelationship with said heating means.

11. In combination with an oven, a control for oven heating means in alow temperature roasting circuit comprising, first cycling switch meansin series with said heating means, said first cycling switch meanspreset to cycle said heating means at a fixed predetermined temperaturein said oven and calibrated to respond accurately to low temperatures insaid oven, second cycling switch means in series with said heating meansand in parallel with said first cycling switch means, said secondcycling switch means calibrated to respond accurately to hightemperatures in said oven, and timing means for selectively placing oneof said switch means in control relationship with said heating means.

References Cited in the file of this patent UNITED STATES PATENTS2,767,293 lord-an et a1 Oct. 16, 1956 2,798,929 Wojcik July 9, 19572,870,313 McCormick Jan. 20, 1959 3,032,636 Schauer May 1, 1962

11. IN COMBINATION WITH AN OVEN, A CONTROL FOR OVEN HEATING MEANS IN ALOW TEMPERATURE ROASTING CIRCUIT COMPRISING, FIRST CYCLING SWITCH MEANSIN SERIES WITH SAID HEATING MEANS, SAID FIRST CYCLING SWITCH MEANSPRESET TO CYCLE SAID HEATING MEANS AT A FIXED PREDETERMINED TEMPERATUREIN SAID OVEN AND CALIBRATED TO RESPOND ACCURATELY TO LOW TEMPERATURES INSAID OVEN, SECOND CYCLING SWITCH MEANS IN SERIES WITH SAID HEATING MEANSAND IN PARALLEL WITH SAID FIRST CYCLING SWITCH MEANS, SECOND CYCLING